1. Field of the Invention
This invention relates to a ceramic which has nonlinear voltage characteristics and is adapted to be used as an over-voltage protecting resistor and a method for producing the same.
2. Description of the Prior Art
Heretofore, over-voltage protecting resistors made of a silicon carbide varistor, a selenium varistor, and the like have been widely used practically. However, the over-voltage resistivity of a semiconductor element such as a diode, a transistor, and a thyristor is far lower than the resistivity of an ordinary electrical machine or piece of equipment, and when protection of the semiconductor element from an over-voltage is desired, a resistor used for that purpose must have the characteristics of a low limiting voltage and the greatest voltage non-linearity. In this respect, both a silicon carbide varistor and a selenium varistor do not have any significant voltage non-linearity, and furthermore, the limiting voltage of a silicon carbide varistor is high while the loading capability of a selenium varistor is low and the size thereof must be large. These features thus are the drawbacks of conventional over-voltage protecting resistors. In addition to the above-described resistors, an arrester having series gaps and an arresting tube are known. These are, however, not suitable for the protection of semi-conductor elements because of their high limiting voltage.